Witnesses report a heavy military presence in Cameroon's commercial hub, Douala, after gunmen dressed in military uniform opened fire on a major bridge to protest the country's longtime president.

Officials say at least five gunmen blockaded the busy Wouri Bridge early Thursday and exchanged gunfire with security forces for about three hours. No injuries were reported.

Authorities say four suspects were taken into custody and another one plunged from the bridge into the river below. Cameroon police said they were interrogating the suspects to determine if they were soldiers.

Security officials say the armed men were carrying signs calling President Paul Biya a "dictator" and saying he must leave "at all costs."

Cameroon is scheduled to hold a presidential election on October 9.

President Biya has ruled the country since 1982 and is widely expected to win another seven-year term. In 2008, the 78-year-old Biya pushed through constitutional changes that eliminated term limits.

The changes triggered anti-government riots in which at least 40 people were killed.

Some opposition supporters have urged Biya to step down and have argued that the old term limits still apply to him.